The nervous system is a complex network of nerves and cells that carry messages between the brain and spinal cord and the rest of the body. It consists of the central nervous system, made up of the brain and spinal cord, and the peripheral nervous system. The nervous system functions through neurons, which transmit electrochemical signals, and neuroglia, or glial cells, which support neuron function. Sensory neurons carry signals from receptors to the central nervous system for processing, while motor neurons then carry signals from the brain and spinal cord to effector cells in the body's tissues and organs.

1. THE
NERVOUS
SYSTEM
Seson Gozo Pagoyo

2. The NERVOUS SYSTEM is a
complex network of nerves and
cells that carry messages to and
from the brain and spinal cord to
various parts of the body. The
nervous system includes both the
central nervous system and
peripheral nervous system.

3. The majority of the nervous system is
tissue made up of two classes of
cells: neurons and neuroglia.
• NEURONS, also known as nerve
cells, communicate within the
body by transmitting
electrochemical signals.
• NEUROGLIA, also known as glial
cells, act as the “helper” cells of
the nervous system.

4. The BRAIN, a soft, wrinkled organ
that weighs about 3 pounds, is
located inside the cranial cavity,
where the bones of the skull surround
and protect it. The brain, the seat of
higher mental functions such as
consciousness, memory, planning,
and voluntary actions, also controls
lower body functions such as the
maintenance of respiration, heart
rate, blood pressure, and digestion.

5. The SPINAL CORD is a long, thin mass
of bundled neurons that carries
information through the vertebral cavity
of the spine beginning at the medulla
oblongata of the brain on its superior end
and continuing inferiorly to the lumbar
region of the spine. The white matter of
the spinal cord functions as the main
conduit of nerve signals to the body from
the brain. The grey matter of the spinal
cord integrates reflexes to stimuli.

6. NERVES are bundles of axons in the
peripheral nervous system (PNS) that act
as information highways to carry signals
between the brain and spinal cord and
the rest of the body. Each axon is
wrapped in a connective tissue sheath
called the endoneurium. Individual axons
of the nerve are bundled into groups of
axons called fascicles, wrapped in a
sheath of connective tissue called the
perineurium.

7. The MENINGES are the protective
coverings of the central nervous system
(CNS). They consist of three layers: the dura
mater, arachnoid mater, and pia mater.
• The dura mater, which means “tough
mother,” is the thickest, toughest, and
most superficial layer of meninges.
• The arachnoid mater, which means
“spider-like mother,” is much thinner and
more delicate than the dura mater.
• The pia mater, which means “tender
mother,” is a thin and delicate layer of
tissue that rests on the outside of the brain
and spinal cord.

8. The space surrounding the organs
of the CNS is filled with a clear fluid
known as CEREBROSPINAL FLUID (CSF).
CSF is formed from blood plasma by
special structures called choroid
plexuses. The choroid plexuses contain
many capillaries lined with epithelial
tissue that filters blood plasma and
allows the filtered fluid to enter the
space around the brain.

9. The nervous system has 3 main
functions: sensory, integration, and
motor.
• The SENSORY FUNCTION of the nervous
system involves collecting information
from sensory receptors that monitor the
body’s internal and external
conditions. These signals are then
passed on to the central nervous
system (CNS) for further processing by
afferent neurons (and nerves).

10. • The process of INTEGRATION is the
processing of the many sensory signals
that are passed into the CNS at any
given time. These signals are
evaluated, compared, used for
decision making, discarded or
committed to memory as deemed
appropriate. Integration takes place in
the gray matter of the brain and spinal
cord and is performed by interneurons.
Many interneurons work together to
form complex networks that provide
this processing power.

11. • MOTOR. Once the networks of
interneurons in the CNS evaluate sensory
information and decide on an action,
they stimulate efferent neurons. Efferent
neurons (also called motor neurons) carry
signals from the gray matter of the CNS
through the nerves of the peripheral
nervous system to effector cells. The
effector may be smooth, cardiac, or
skeletal muscle tissue or glandular tissue.
The effector then releases a hormone or
moves a part of the body to respond to
the stimulus.